The activists, mostly North Korean defectors, floated the balloons containing leaflets and other propaganda materials denouncing the impoverished state from an unsuspected site near the border later in the day despite warnings of a direct strike from the North, Asahi Shimbun reports.

“We could not delay our plans to send anti-North Korea leaflets because it is our love toward our northern borders,” the activists wrote in a statement posted in Seoul-based Free North Korea Radio’s website, adding that they wanted North Koreans to “know the true nature of their country”.

According to Korea JoongAngDaily, around 820 local residents in the area were asked to evacuate to underground shelters on Sunday after the South Korean military detected North Korean soldiers deployed near the border with artillery pointed to the South.

“They threatened us before but dispatching the soldiers was new,” an South Korean military official said.

South Korea’s Defense Ministry said there were no suspicious activities in the North, but said it was closely monitoring movement from across the border.